The invention relates to a method of treating a contaminated aqueous solution and more particularly to a method of treating an aqueous solution contaminated with cations.
Industrial facilities and equipment contaminated with radioactive metals such as cobalt-58 and cobalt-60 or with heavy metals such as mercury and lead and the like generally are cleaned before they are to be maintained or decommissioned. Typically, an aqueous solution containing a carboxylic complexing agent such as a chelating agent, soap or detergent is circulated through the equipment to solubilize and transport the contaminants from the equipment. See, for example, M. E. Pick et al., "Chemical Decontamination Of Water Reactors. CEGB Developments And The International Scene", Nuclear Energy, 1983, 22, No. 6, December, pages 433-444, which discusses CAN-DECON, LOMI and other dilute chemical decontamination processes that have been employed to decontaminate water cooled reactor facilities or components.
The contaminants in the aqueous cleaning solution must then be immobilized before the water can be released to the environment and the metals can be buried at a permanent disposal site. Thus, the metal contaminants may be adsorbed on ion exchange resins or activated carbon beds and then buried. In other cases, the metals may be precipitated from the solution with precipitating agents and filter aids and then the metals buried together with the precipitating agents and filter aids.
A relatively small amount of waste generates a relatively large volume of waste which is very costly to bury. For example, at least about 40 liters of solid waste volume will be generated by the treatment of only 1000 gallons of water contaminated with 1000 parts per million (ppm) of metal cations with an ion exchange resin or activated carbon. The use of precipitating agents may generate less volume, but no less than about 20 liters. In addition, nuclear wastes may need to be stored onsite in interim storage facilities for long periods of time until a burial site becomes available. For hazardous wastes, a "land ban" on waste disposal has required that ion exchange resins and activated carbon containing hazardous wastes be first treated at costs of from about $300 to about $2,000 per ton before disposal.